There are two things that children can control in their little lives - eating and pottying. And he is showing you point blank that since he can't control ANYTHING else in your household, including your baby usurping his place, he will resist you at all costs over this pottying thing.
So what are you going to do about it? Fight him harder? Pull more muscles?
You are making a BIG mistake in your thinking. You should never have tried to train him when he didn't want to be trained. You were trying to train him to make your life easier. You wanted him to do it for YOU, not for him. Now you're paying the price.
Stop all the training for now. Put diapers, and diapers only, on him. No Pullups. Don't put bigger diapers on him either - let them be a little tight and uncomfortable. When he pulls at them, tell him that when he is a big boy, he can wear big boy pants and they will feel nice and soft and comfy! And say NO MORE than that. Wait til he has had his 3rd birthday. And THEN take him to the store on a Friday afternoon or night and let HIM pick out big boy pants, with any character on them that he wants.
From today until August when you buy him the big boy pants, don't give him ANY candy AT ALL. NONE. On Saturday morning right after breakfast, the morning after your buy the big boy pants, sit him down and show him a big bag of M&M's. When he sees this bag of M&M's, his eyes will POP! Give him ONE M&M. He will love it. Then ask him if he would like to earn more M&M's. Pull out the big boy pants and have him take them out of the wrapper. Count 5 M&M's out of the bag and line them up in front of you (no touching!). Tell him for peeing in the potty, he gets 5 M&M's. Then count out 5 more and line 'em up - for pooping in the potty, you get 10!! Wow! And he can wear his favorite big boy pants while he is earning his M&M's. Which pair do you want to wear first?
Then ply him with water and milk throughout the day, fiber and prunes to make sure his poop is soft, and use a timer set every hour to ring in front of him. When the timer goes off, ask him if he'd like to try to earn his M&M's. Even if he dribbles a couple of drops, make a big deal out of it and give him 5 M&M's. The prunes and fiber and water you give him will keep him from getting constipated, so don't worry about the candy giving him trouble.
Stay home all weekend and do this. If he has an accident, don't fuss or make a big deal of it. Just help clean him up. Put a diaper back on him for night time. Night time training is not the same as daytime and you should NOT try both together. He should be very comfortable pottying during the day before you even begin to try night time training.
After about a week of success, don't mention the M&M's unless he asks. Then at some point, you have "run out". OR, you can say "Well, honey, you don't really need any more M&M's - you are a big boy now. But would you like to enjoy some with mommy after lunch?" Then share some together, and voila, the bag is empty and there are no more M&M's anyway. (At least, that HE knows of!)
DO NOT MAKE him go to the potty. This idea of him pooping on the potty at least some of the time is for the birds. You don't start until he is ready. You give him an incentive for wanting to go and for trying to go. You make it stress-free. You give him accolades for going, you tell him that you know he is sad that he made a mistake, but it's okay, because everyone makes mistakes sometimes. You never punish because he didn't make it to the bathroom. You let him figure out that being wet or dirty makes him feel uncomfortable. If you put him in Pullups, he won't learn that uncomfortable feeling. If you put bigger diapers on him that fit, he won't learn that uncomfortable feeling. If he never gets his sheets wet, he won't have any incentive to learn to sleep train (when he's older - 3 is too young to expect that he can hold it all night.)
You have to let him OWN this and learn it. And that means several weeks of giving him incentives and letting him handle his emotions and being willing to try without YOU jumping on him. Take yourself and YOUR wishes out of this. This is all about HIM.
Changing your point of view and your attitude is what will make him decide to work with you. I hope you are willing to do this.
Dawn